I was wondering...how do you make a lake on the secondary planet??.....
do not confuse this with applying water shader to the terrain...
probably by placing the lake object somewhere on the surface of the planet. Prety literaly. You'd need to calculate the exact location of the XYZ location of your watter so that it's on the other planet.
You can (and probably should) also assign the lake to the other planet on the Planet tab.
- Oshyan